Preheat the oven to 350°F (175°C). Grease a 9x5-inch loaf pan and line with parchment paper.
In a bowl, whisk together flour, baking soda, and salt. Set aside.
In another bowl, whisk melted butter and brown sugar until smooth. Add eggs, mashed bananas, Greek yogurt, and vanilla extract, and mix until combined.
Gradually fold in the dry ingredients until just combined—don’t overmix!
In a small bowl, mix granulated sugar and cinnamon for the swirl.
Layer the batter: Pour half of the batter into the loaf pan, sprinkle half of the cinnamon-sugar mixture, then repeat with the remaining batter and cinnamon-sugar. Swirl with a knife.
Bake for 50-55 minutes, or until a toothpick inserted in the center comes out clean.
Let the bread cool in the pan for 10-15 minutes, then transfer to a wire rack.
Slice, serve, and enjoy!